diff --git a/build.zig b/build.zig
index a16115a2de..b1622a32de 100644
--- a/build.zig
+++ b/build.zig
@@ -232,8 +232,8 @@ pub fn build(b: *std.Build) !void {
         \\
     , .{medium}));
 
-    // TODO(zig): using getEmittedIncludeTree() is ugly af. we want run_preprocessor()
-    // to use the std.build.Module include_path thing
+    // TODO(zig): using getEmittedIncludeTree() is ugly af. we want unittests
+    // to reuse the std.build.Module include_path thing
     const include_path = [_]LazyPath{
         b.path("src/"),
         gen_config.getDirectory(),
@@ -245,7 +245,7 @@ pub fn build(b: *std.Build) !void {
         treesitter.artifact("tree-sitter").getEmittedIncludeTree(),
     };
 
-    const gen_headers, const funcs_data = try gen.nvim_gen_sources(b, nlua0, &nvim_sources, &nvim_headers, &api_headers, &include_path, target, versiondef_git, version_lua);
+    const gen_headers, const funcs_data = try gen.nvim_gen_sources(b, nlua0, &nvim_sources, &nvim_headers, &api_headers, versiondef_git, version_lua);
 
     const test_config_step = b.addWriteFiles();
     _ = test_config_step.add("test/cmakeconfig/paths.lua", try test_config(b));
diff --git a/src/gen/c_grammar.lua b/src/gen/c_grammar.lua
index feef536337..356d5f80cd 100644
--- a/src/gen/c_grammar.lua
+++ b/src/gen/c_grammar.lua
@@ -160,6 +160,8 @@ local typed_container = P({
         )
     + Cg(opt(P('*')) * P('Dict')) * paren(C(id))
     + Cg(opt(P('*')) * P('DictAs')) * paren(C(id))
+    + Cg(opt(P('*')) * P('Set')) * paren(C(id))
+    + Cg(opt(P('*')) * P('PMap')) * paren(C(id))
   ),
   -- Remove captures here (with / 0 ) as api_types will recursively run parse the type.
   TY = Cg(V('S') / 0 + V('ID')),
diff --git a/src/gen/gen_declarations.lua b/src/gen/gen_declarations.lua
index 582ac756b4..c0fd0381e8 100644
--- a/src/gen/gen_declarations.lua
+++ b/src/gen/gen_declarations.lua
@@ -71,17 +71,13 @@ end
 --- @return string[] static
 --- @return string[] non_static
 --- @return boolean any_static
-local function gen_declarations(fname, text)
+local function gen_declarations(text)
   local non_static = {} --- @type string[]
   local static = {} --- @type string[]
 
-  local neededfile = fname:match('[^/]+$')
-  local curfile = nil
   local any_static = false
   for _, node in ipairs(grammar:match(text)) do
-    if node[1] == 'preproc' then
-      curfile = node.content:match('^%a* %d+ "[^"]-/?([^"/]+)"') or curfile
-    elseif node[1] == 'proto' and curfile == neededfile then
+    if node[1] == 'proto' then
       local node_text = text:sub(node.pos, node.endpos - 1)
       local declaration = process_decl(node_text)
 
@@ -102,31 +98,27 @@ end
 local usage = [[
 Usage:
 
-    gen_declarations.lua definitions.c static.h non-static.h definitions.i
+    gen_declarations.lua definitions.c static.h non-static.h
 
 Generates declarations for a C file definitions.c, putting declarations for
 static functions into static.h and declarations for non-static functions into
-non-static.h. File `definitions.i' should contain an already preprocessed
-version of definitions.c and it is the only one which is actually parsed,
-definitions.c is needed only to determine functions from which file out of all
-functions found in definitions.i are needed and to generate an IWYU comment.
+non-static.h. Also generate an IWYU comment.
 ]]
 
 local function main()
   local fname = arg[1]
   local static_fname = arg[2]
   local non_static_fname = arg[3]
-  local preproc_fname = arg[4]
-  local static_basename = arg[5]
+  local static_basename = arg[4]
 
-  if fname == '--help' or #arg < 5 then
+  if fname == '--help' or #arg < 4 then
     print(usage)
     os.exit()
   end
 
-  local text = assert(read_file(preproc_fname))
+  local text = assert(read_file(fname))
 
-  local static_decls, non_static_decls, any_static = gen_declarations(fname, text)
+  local static_decls, non_static_decls, any_static = gen_declarations(text)
 
   local static = {} --- @type string[]
   if fname:find('.*/src/nvim/.*%.h$') then
diff --git a/src/gen/gen_steps.zig b/src/gen/gen_steps.zig
index 7f2e0faea6..7aeec2a71c 100644
--- a/src/gen/gen_steps.zig
+++ b/src/gen/gen_steps.zig
@@ -9,8 +9,6 @@ pub fn nvim_gen_sources(
     nvim_sources: *std.ArrayList(SourceItem),
     nvim_headers: *std.ArrayList([]u8),
     api_headers: *std.ArrayList(LazyPath),
-    include_path: []const LazyPath,
-    target: std.Build.ResolvedTarget,
     versiondef_git: LazyPath,
     version_lua: LazyPath,
 ) !struct { *std.Build.Step.WriteFile, LazyPath } {
@@ -19,12 +17,12 @@ pub fn nvim_gen_sources(
     for (nvim_sources.items) |s| {
         const api_export = if (s.api_export) api_headers else null;
         const input_file = b.path(b.fmt("src/nvim/{s}", .{s.name}));
-        _ = try generate_header_for(b, s.name, input_file, api_export, nlua0, include_path, target, gen_headers, false);
+        _ = try generate_header_for(b, s.name, input_file, api_export, nlua0, gen_headers, false);
     }
 
     for (nvim_headers.items) |s| {
         const input_file = b.path(b.fmt("src/nvim/{s}", .{s}));
-        _ = try generate_header_for(b, s, input_file, null, nlua0, include_path, target, gen_headers, true);
+        _ = try generate_header_for(b, s, input_file, null, nlua0, gen_headers, true);
     }
 
     {
@@ -95,17 +93,17 @@ pub fn nvim_gen_sources(
         const gen_step = b.addRunArtifact(nlua0);
         gen_step.addFileArg(b.path("src/gen/gen_api_ui_events.lua"));
         gen_step.addFileArg(b.path("src/nvim/api/ui_events.in.h"));
-        _ = try gen_header_with_header(b, gen_step, "ui_events_call.generated.h", nlua0, include_path, target, gen_headers);
-        _ = try gen_header_with_header(b, gen_step, "ui_events_remote.generated.h", nlua0, include_path, target, gen_headers);
+        _ = try gen_header_with_header(b, gen_step, "ui_events_call.generated.h", nlua0, gen_headers);
+        _ = try gen_header_with_header(b, gen_step, "ui_events_remote.generated.h", nlua0, gen_headers);
         const ui_metadata = gen_step.addOutputFileArg("ui_metadata.mpack");
-        _ = try gen_header_with_header(b, gen_step, "ui_events_client.generated.h", nlua0, include_path, target, gen_headers);
+        _ = try gen_header_with_header(b, gen_step, "ui_events_client.generated.h", nlua0, gen_headers);
         break :ui_step ui_metadata;
     };
 
     const funcs_metadata = api_step: {
         const gen_step = b.addRunArtifact(nlua0);
         gen_step.addFileArg(b.path("src/gen/gen_api_dispatch.lua"));
-        _ = try gen_header_with_header(b, gen_step, "api/private/dispatch_wrappers.generated.h", nlua0, include_path, target, gen_headers);
+        _ = try gen_header_with_header(b, gen_step, "api/private/dispatch_wrappers.generated.h", nlua0, gen_headers);
         _ = gen_header(b, gen_step, "api/private/api_metadata.generated.h", gen_headers);
         const funcs_metadata = gen_step.addOutputFileArg("funcs_metadata.mpack");
         _ = gen_header(b, gen_step, "lua_api_c_bindings.generated.h", gen_headers);
@@ -153,13 +151,11 @@ fn gen_header_with_header(
     gen_step: *std.Build.Step.Run,
     name: []const u8,
     nlua0: *std.Build.Step.Compile,
-    include_path: []const LazyPath,
-    target: ?std.Build.ResolvedTarget,
     gen_headers: *std.Build.Step.WriteFile,
 ) !std.Build.LazyPath {
     if (name.len < 12 or !std.mem.eql(u8, ".generated.h", name[name.len - 12 ..])) return error.InvalidBaseName;
     const h = gen_header(b, gen_step, name, gen_headers);
-    _ = try generate_header_for(b, b.fmt("{s}.h", .{name[0 .. name.len - 12]}), h, null, nlua0, include_path, target, gen_headers, false);
+    _ = try generate_header_for(b, b.fmt("{s}.h", .{name[0 .. name.len - 12]}), h, null, nlua0, gen_headers, false);
     return h;
 }
 
@@ -169,55 +165,17 @@ pub const PreprocessorOptions = struct {
     target: ?std.Build.ResolvedTarget = null,
 };
 
-fn run_preprocessor(
-    b: *std.Build,
-    src: LazyPath,
-    output_name: []const u8,
-    options: PreprocessorOptions,
-) !LazyPath {
-    const run_step = std.Build.Step.Run.create(b, b.fmt("preprocess to get {s}", .{output_name}));
-    run_step.addArgs(&.{ b.graph.zig_exe, "cc", "-E" });
-    run_step.addFileArg(src);
-    run_step.addArg("-o");
-    const output = run_step.addOutputFileArg(output_name);
-    // upstream issue: include path logic for addCSourceFiles and TranslateC is _very_ different
-    for (options.include_dirs) |include_dir| {
-        run_step.addArg("-I");
-        run_step.addDirectoryArg(include_dir);
-    }
-    for (options.c_macros) |c_macro| {
-        run_step.addArg(b.fmt("-D{s}", .{c_macro}));
-    }
-    if (options.target) |t| {
-        if (!t.query.isNative()) {
-            run_step.addArgs(&.{
-                "-target", try t.query.zigTriple(b.allocator),
-            });
-        }
-    }
-    run_step.addArgs(&.{ "-MMD", "-MF" });
-    _ = run_step.addDepFileOutputArg(b.fmt("{s}.d", .{output_name}));
-    return output;
-}
-
 fn generate_header_for(
     b: *std.Build,
     name: []const u8,
     input_file: LazyPath,
     api_export: ?*std.ArrayList(LazyPath),
     nlua0: *std.Build.Step.Compile,
-    include_path: []const LazyPath,
-    target: ?std.Build.ResolvedTarget,
     gen_headers: *std.Build.Step.WriteFile,
     nvim_header: bool,
 ) !*std.Build.Step.Run {
     if (name.len < 2 or !(std.mem.eql(u8, ".c", name[name.len - 2 ..]) or std.mem.eql(u8, ".h", name[name.len - 2 ..]))) return error.InvalidBaseName;
     const basename = name[0 .. name.len - 2];
-    const i_file = try run_preprocessor(b, input_file, b.fmt("{s}.i", .{basename}), .{
-        .include_dirs = include_path,
-        .c_macros = &.{ "_GNU_SOURCE", "ZIG_BUILD" },
-        .target = target,
-    });
     const run_step = b.addRunArtifact(nlua0);
     run_step.addFileArg(b.path("src/gen/gen_declarations.lua"));
     run_step.addFileArg(input_file);
@@ -232,7 +190,6 @@ fn generate_header_for(
         }
     }
 
-    run_step.addFileArg(i_file);
     run_step.addArg(gen_name);
     return run_step;
 }
diff --git a/src/nvim/CMakeLists.txt b/src/nvim/CMakeLists.txt
index 1b7341560d..910bd1effe 100644
--- a/src/nvim/CMakeLists.txt
+++ b/src/nvim/CMakeLists.txt
@@ -84,6 +84,7 @@ if(NOT MSVC)
     -Wmissing-noreturn
     -Wmissing-format-attribute
     -Wmissing-prototypes
+    -Wno-unused-function # because #35129
     -fsigned-char)
 
   # For O_CLOEXEC, O_DIRECTORY, and O_NOFOLLOW flags on older systems
@@ -465,37 +466,19 @@ endif()
 # Header generation
 #-------------------------------------------------------------------------------
 
-get_target_property(prop main_lib INTERFACE_COMPILE_DEFINITIONS)
-if(NOT "${prop}" STREQUAL "prop-NOTFOUND")
-  foreach(gen_cdef ${prop})
-    if(NOT ${gen_cdef} MATCHES "INCLUDE_GENERATED_DECLARATIONS")
-      list(APPEND gen_cflags "-D${gen_cdef}")
-    endif()
-  endforeach()
-endif()
-
 get_directory_property(targets BUILDSYSTEM_TARGETS)
 foreach(target ${targets})
   get_target_property(prop ${target} INTERFACE_INCLUDE_DIRECTORIES)
   if(NOT "${prop}" STREQUAL "prop-NOTFOUND")
     message(STATUS "${target} props '${prop}'")
     foreach(gen_include ${prop})
-      list(APPEND gen_cflags "-I${gen_include}")
       list(APPEND TEST_INCLUDE_DIRS "${gen_include}")
     endforeach()
   endif()
 endforeach()
 
-list(REMOVE_DUPLICATES gen_cflags)
 list(REMOVE_DUPLICATES TEST_INCLUDE_DIRS)
 
-if(APPLE AND CMAKE_OSX_SYSROOT)
-  list(APPEND gen_cflags "-isysroot" "${CMAKE_OSX_SYSROOT}")
-endif()
-if(MSVC)
-  list(APPEND gen_cflags -wd4003)
-endif()
-
 set(NVIM_VERSION_GIT_H ${PROJECT_BINARY_DIR}/cmake.config/auto/versiondef_git.h)
 add_custom_target(update_version_stamp
   COMMAND ${CMAKE_COMMAND}
@@ -558,13 +541,6 @@ foreach(sfile ${NVIM_SOURCES}
     set(gf_h_h "${GENERATED_INCLUDES_DIR}/${r}.h.generated.h")
     set(gf_h_h_out "${gf_h_h}")
   endif()
-  set(gf_i "${GENERATED_DIR}/${f}.i")
-
-  if(MSVC)
-    set(PREPROC_OUTPUT /P /Fi${gf_i} /nologo)
-  else()
-    set(PREPROC_OUTPUT -w -E -o ${gf_i})
-  endif()
 
   set(depends "${HEADER_GENERATOR}" "${sfile}" "${LUA_GEN_DEPS}" "${GENERATOR_C_GRAMMAR}")
   if("${f}" STREQUAL "version.c")
@@ -573,8 +549,7 @@ foreach(sfile ${NVIM_SOURCES}
   endif()
   add_custom_command(
     OUTPUT "${gf_c_h}" ${gf_h_h_out}
-    COMMAND ${CMAKE_C_COMPILER} ${sfile} ${PREPROC_OUTPUT} ${gen_cflags}
-    COMMAND ${LUA_GEN} "${HEADER_GENERATOR}" "${sfile}" "${gf_c_h}" "${gf_h_h}" "${gf_i}" "${gf_basename}"
+    COMMAND ${LUA_GEN} "${HEADER_GENERATOR}" "${sfile}" "${gf_c_h}" "${gf_h_h}" "${gf_basename}"
     DEPENDS ${depends})
   list(APPEND NVIM_GENERATED_FOR_SOURCES "${gf_c_h}")
   if (NOT ${sfile} IN_LIST NVIM_HEADERS)
diff --git a/src/nvim/arabic.h b/src/nvim/arabic.h
index ac27153a37..2d09531331 100644
--- a/src/nvim/arabic.h
+++ b/src/nvim/arabic.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdbool.h>
+
 #define ARABIC_CHAR(ch)            (((ch) & 0xFF00) == 0x0600)
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
diff --git a/src/nvim/base64.c b/src/nvim/base64.c
index 99d3c5a33e..2de6d1f1f6 100644
--- a/src/nvim/base64.c
+++ b/src/nvim/base64.c
@@ -31,7 +31,7 @@ static const uint8_t char_to_index[256] = {
 };
 
 #ifndef HAVE_BE64TOH
-static inline uint64_t htobe64(uint64_t host_64bits)
+static inline uint64_t vim_htobe64(uint64_t host_64bits)
 {
 # ifdef ORDER_BIG_ENDIAN
   return host_64bits;
@@ -45,7 +45,7 @@ static inline uint64_t htobe64(uint64_t host_64bits)
 # endif
 }
 
-static inline uint32_t htobe32(uint32_t host_32bits)
+static inline uint32_t vim_htobe32(uint32_t host_32bits)
 {
 # ifdef ORDER_BIG_ENDIAN
   return host_32bits;
@@ -58,6 +58,8 @@ static inline uint32_t htobe32(uint32_t host_32bits)
   return ret;
 # endif
 }
+# define htobe64 vim_htobe64
+# define htobe32 vim_htobe32
 #endif
 
 /// Encode a string using Base64.
diff --git a/src/nvim/lua/converter.c b/src/nvim/lua/converter.c
index 98d99c1c95..27c0533713 100644
--- a/src/nvim/lua/converter.c
+++ b/src/nvim/lua/converter.c
@@ -729,18 +729,11 @@ void nlua_push_Array(lua_State *lstate, const Array array, int flags)
   }
 }
 
-#define GENERATE_INDEX_FUNCTION(type) \
-  void nlua_push_##type(lua_State *lstate, const type item, int flags) \
-  FUNC_ATTR_NONNULL_ALL \
-  { \
-    lua_pushnumber(lstate, (lua_Number)(item)); \
-  }
-
-GENERATE_INDEX_FUNCTION(Buffer)
-GENERATE_INDEX_FUNCTION(Window)
-GENERATE_INDEX_FUNCTION(Tabpage)
-
-#undef GENERATE_INDEX_FUNCTION
+void nlua_push_handle(lua_State *lstate, const handle_T item, int flags)
+  FUNC_ATTR_NONNULL_ALL
+{
+  lua_pushnumber(lstate, (lua_Number)(item));
+}
 
 /// Convert given Object to Lua value
 ///
diff --git a/src/nvim/lua/converter.h b/src/nvim/lua/converter.h
index d1ba61bcee..fb726db9cf 100644
--- a/src/nvim/lua/converter.h
+++ b/src/nvim/lua/converter.h
@@ -9,6 +9,10 @@
 #define nlua_pop_Window nlua_pop_handle
 #define nlua_pop_Tabpage nlua_pop_handle
 
+#define nlua_push_Buffer nlua_push_handle
+#define nlua_push_Window nlua_push_handle
+#define nlua_push_Tabpage nlua_push_handle
+
 /// Flags for nlua_push_*() functions.
 enum {
   kNluaPushSpecial = 0x01,   ///< Use lua-special-tbl when necessary
diff --git a/src/nvim/lua/stdlib.h b/src/nvim/lua/stdlib.h
index 26e96055ae..20cea44a04 100644
--- a/src/nvim/lua/stdlib.h
+++ b/src/nvim/lua/stdlib.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <lua.h>  // IWYU pragma: keep
+#include <stdbool.h>
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "lua/stdlib.h.generated.h"
diff --git a/src/nvim/main.h b/src/nvim/main.h
index 5ae5d98de4..418b41eafc 100644
--- a/src/nvim/main.h
+++ b/src/nvim/main.h
@@ -47,6 +47,11 @@ typedef struct {
   bool had_stdin_file;                  // explicit - as a file to edit
 } mparm_T;
 
+#if defined(MSWIN) && !defined(ENABLE_ASAN_UBSAN)
+# define __asan_default_options vim__asan_default_options
+# define __ubsan_default_options vim__ubsan_default_options
+#endif
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "main.h.generated.h"
 #endif
diff --git a/src/nvim/mark.c b/src/nvim/mark.c
index 71fc119343..e5d775692d 100644
--- a/src/nvim/mark.c
+++ b/src/nvim/mark.c
@@ -717,11 +717,7 @@ static void fname2fnum(xfmark_T *fm)
 
   // First expand "~/" in the file name to the home directory.
   // Don't expand the whole name, it may contain other '~' chars.
-#ifdef BACKSLASH_IN_FILENAME
-  if (fm->fname[0] == '~' && (fm->fname[1] == '/' || fm->fname[1] == '\\')) {
-#else
-  if (fm->fname[0] == '~' && (fm->fname[1] == '/')) {
-#endif
+  if (fm->fname[0] == '~' && vim_ispathsep_nocolon(fm->fname[1])) {
     size_t len = expand_env("~/", NameBuff, MAXPATHL);
     xstrlcpy(NameBuff + len, fm->fname + 2, MAXPATHL - len);
   } else {
diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index aae5445805..21bd1dcd0e 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1174,7 +1174,7 @@ bool utf_printable(int c)
 
 // Return true if "c" is in "table".
 static bool intable(const struct interval *table, size_t n_items, int c)
-  FUNC_ATTR_PURE
+  FUNC_ATTR_CONST
 {
   assert(n_items > 0);
   // first quick check for Latin1 etc. characters
@@ -1202,11 +1202,11 @@ static bool intable(const struct interval *table, size_t n_items, int c)
 // Return true for characters that can be displayed in a normal way.
 // Only for characters of 0x100 and above!
 bool utf_printable(int c)
-  FUNC_ATTR_PURE
+  FUNC_ATTR_CONST
 {
   // Sorted list of non-overlapping intervals.
   // 0xd800-0xdfff is reserved for UTF-16, actually illegal.
-  static struct interval nonprint[] = {
+  static const struct interval nonprint[] = {
     { 0x070f, 0x070f }, { 0x180b, 0x180e }, { 0x200b, 0x200f }, { 0x202a, 0x202e },
     { 0x2060, 0x206f }, { 0xd800, 0xdfff }, { 0xfeff, 0xfeff }, { 0xfff9, 0xfffb },
     { 0xfffe, 0xffff }
diff --git a/src/nvim/msgpack_rpc/channel.c b/src/nvim/msgpack_rpc/channel.c
index ee2a502ebb..531ec75759 100644
--- a/src/nvim/msgpack_rpc/channel.c
+++ b/src/nvim/msgpack_rpc/channel.c
@@ -33,6 +33,10 @@
 #include "nvim/ui.h"
 #include "nvim/ui_client.h"
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "msgpack_rpc/channel.c.generated.h"
+#endif
+
 #ifdef NVIM_LOG_DEBUG
 # define REQ "[request]  "
 # define RES "[response] "
@@ -66,10 +70,6 @@ static void log_notify(char *dir, uint64_t channel_id, const char *name)
 # define log_notify(...)
 #endif
 
-#ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "msgpack_rpc/channel.c.generated.h"
-#endif
-
 void rpc_init(void)
 {
   ch_before_blocking_events = multiqueue_new_child(main_loop.events);
diff --git a/src/nvim/msgpack_rpc/server.h b/src/nvim/msgpack_rpc/server.h
index 71b578a14b..96380ddd29 100644
--- a/src/nvim/msgpack_rpc/server.h
+++ b/src/nvim/msgpack_rpc/server.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>  // IWYU pragma: keep
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
diff --git a/src/nvim/os/dl.h b/src/nvim/os/dl.h
index 0787c7fe46..fe93f3d640 100644
--- a/src/nvim/os/dl.h
+++ b/src/nvim/os/dl.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdbool.h>
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/dl.h.generated.h"
 #endif
diff --git a/src/nvim/os/fs.c b/src/nvim/os/fs.c
index f7ef3a5235..288c000dde 100644
--- a/src/nvim/os/fs.c
+++ b/src/nvim/os/fs.c
@@ -245,14 +245,12 @@ bool os_can_exe(const char *name, char **abspath, bool use_path)
 {
   if (!use_path || gettail_dir(name) != name) {
 #ifdef MSWIN
-    if (is_executable_ext(name, abspath)) {
+    return is_executable_ext(name, abspath);
 #else
     // Must have path separator, cannot execute files in the current directory.
-    if ((use_path || gettail_dir(name) != name)
-        && is_executable(name, abspath)) {
+    return ((use_path || gettail_dir(name) != name)
+            && is_executable(name, abspath));
 #endif
-      return true;
-    }
     return false;
   }
 
@@ -339,6 +337,8 @@ static bool is_executable_ext(const char *name, char **abspath)
   }
   return false;
 }
+#else
+# define is_executable_ext is_executable
 #endif
 
 /// Checks if a file is in `$PATH` and is executable.
@@ -384,11 +384,7 @@ static bool is_executable_in_path(const char *name, char **abspath)
     xmemcpyz(buf, p, (size_t)(e - p));
     (void)append_path(buf, name, bufsize);
 
-#ifdef MSWIN
     if (is_executable_ext(buf, abspath)) {
-#else
-    if (is_executable(buf, abspath)) {
-#endif
       rv = true;
       goto end;
     }
diff --git a/src/nvim/os/proc.c b/src/nvim/os/proc.c
index 053f5f3ba0..033a82b0f1 100644
--- a/src/nvim/os/proc.c
+++ b/src/nvim/os/proc.c
@@ -48,7 +48,7 @@
 #endif
 
 #ifdef MSWIN
-static bool os_proc_tree_kill_rec(HANDLE proc, int sig)
+static bool os_proc_tree_kill_rec(void *proc, int sig)
 {
   if (proc == NULL) {
     return false;
diff --git a/src/nvim/os/proc.h b/src/nvim/os/proc.h
index 1831f21cc3..baf8e77d4e 100644
--- a/src/nvim/os/proc.h
+++ b/src/nvim/os/proc.h
@@ -2,9 +2,7 @@
 
 #include <stddef.h>  // IWYU pragma: keep
 
-#ifdef MSWIN
-# include "nvim/api/private/defs.h"  // IWYU pragma: keep
-#endif
+#include "nvim/api/private/defs.h"  // IWYU pragma: keep
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/proc.h.generated.h"
diff --git a/src/nvim/os/pty_proc_unix.c b/src/nvim/os/pty_proc_unix.c
index 98d6f7a2f9..7ea6c449ff 100644
--- a/src/nvim/os/pty_proc_unix.c
+++ b/src/nvim/os/pty_proc_unix.c
@@ -56,8 +56,8 @@ int forkpty(int *, char *, const struct termios *, const struct winsize *);
 // inclusion of the header even though it gets include out of order.
 # include <sys/stropts.h>
 
-static int openpty(int *amaster, int *aslave, char *name, struct termios *termp,
-                   struct winsize *winp)
+static int vim_openpty(int *amaster, int *aslave, char *name, struct termios *termp,
+                       struct winsize *winp)
 {
   int slave = -1;
   int master = open("/dev/ptmx", O_RDWR);
@@ -117,7 +117,7 @@ error:
   return -1;
 }
 
-static int login_tty(int fd)
+static int vim_login_tty(int fd)
 {
   setsid();
   if (ioctl(fd, TIOCSCTTY, NULL) == -1) {
@@ -134,10 +134,10 @@ static int login_tty(int fd)
   return 0;
 }
 
-static pid_t forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp)
+pid_t vim_forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp)
 {
   int master, slave;
-  if (openpty(&master, &slave, name, termp, winp) == -1) {
+  if (vim_openpty(&master, &slave, name, termp, winp) == -1) {
     return -1;
   }
 
@@ -149,7 +149,7 @@ static pid_t forkpty(int *amaster, char *name, struct termios *termp, struct win
     return -1;
   case 0:
     close(master);
-    login_tty(slave);
+    vim_login_tty(slave);
     return 0;
   default:
     close(slave);
@@ -157,7 +157,7 @@ static pid_t forkpty(int *amaster, char *name, struct termios *termp, struct win
     return pid;
   }
 }
-
+# define forkpty vim_forkpty
 #endif
 
 /// @returns zero on success, or negative error code
diff --git a/src/nvim/os/time.h b/src/nvim/os/time.h
index b4d82d8002..1187a2143a 100644
--- a/src/nvim/os/time.h
+++ b/src/nvim/os/time.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>  // IWYU pragma: keep
 #include <time.h>  // IWYU pragma: keep
 
diff --git a/src/nvim/sha256.h b/src/nvim/sha256.h
index 942836a411..f2354298ce 100644
--- a/src/nvim/sha256.h
+++ b/src/nvim/sha256.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>  // IWYU pragma: keep
 #include <stdint.h>
 
diff --git a/src/nvim/shada.c b/src/nvim/shada.c
index a9bda0100a..ea04ac560e 100644
--- a/src/nvim/shada.c
+++ b/src/nvim/shada.c
@@ -3003,7 +3003,7 @@ static void shada_free_shada_entry(ShadaEntry *const entry)
 }
 
 #ifndef HAVE_BE64TOH
-static inline uint64_t be64toh(uint64_t big_endian_64_bits)
+static inline uint64_t vim_be64toh(uint64_t big_endian_64_bits)
 {
 # ifdef ORDER_BIG_ENDIAN
   return big_endian_64_bits;
@@ -3019,6 +3019,7 @@ static inline uint64_t be64toh(uint64_t big_endian_64_bits)
   return ret;
 # endif
 }
+# define be64toh vim_be64toh
 #endif
 
 /// Read given number of bytes into given buffer, display error if needed
diff --git a/src/nvim/spellsuggest.h b/src/nvim/spellsuggest.h
index 40e51a0f88..45ff6af647 100644
--- a/src/nvim/spellsuggest.h
+++ b/src/nvim/spellsuggest.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdbool.h>
+
 #include "nvim/garray_defs.h"  // IWYU pragma: keep
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS